You Have to Be Careful in the Land of the Free by James Kelman448pp, Hamish Hamilton, £10.99

James Kelman is habitually compared favourably to literary giants such as Kafka, Beckett and Zola. While it's interesting to look at stylistic or contextual commonalties, this approach obscures as much as it illuminates our understanding of his work. Kelman is a true original; a highly engaged writer very much of his place and times, and trying to understand him by his antecedents is ultimately a futile exercise.

Kelman always manages to write challenging and important books; each one seems to make him even more essential. His prose perpetually reminds us that in this world, outside of our media-generated superficialities and stereotypes, classes and cultures are less cognisant with each other than ever. Ironically, some of the responses to this book will doubtless provide an illustration of this. A depressing number of critics will view You Have to Be Careful purely as a tale of a Scotsman on the piss in the US, reminiscing about his life and trying to make that flight back home, told in a largely unbroken "stream of consciousness" narrative. And so it is - in much the same way that Moby-Dick is about a big whale.

The narrator of this novel is a Glaswegian male called Jeremiah. As with everything Kelman does, there is a reason for this unlikely moniker. Subversively, Jeremiah is given "Uhmerkin" roots, the half-arsed notion of searching for them originally enticing him to the US from "Skallin". However, you do have to be careful in the land of the free, and though he looks close to the Waspish ideal, Jeremiah - who has acquired dependents on his US sojourn - finds himself a "non-assimilated alien" and trapped by that status on the margins of American economy and society. And as he discovers, it's a far from lonely place to be in today's USA.

In true Weedgie style, Jeremiah gives it narrative loads, by turns intense, mischievous and sentimental, as he becomes the presence you want to avoid in the pub. Though craving company, he's still self-aware enough to avoid a fellow Scot in similar circumstances, a situation we've all been in on our travels. You come to realise that's why God made the replica football strip; that guy wearing the green and white hooped top sitting in at least one bar in every city from San Francisco to Sydney is on his own for a good reason.

But Kelman has never been afraid of exposing his characters' vanities and foibles, without ever compromising their essential humanity. Yet again one of his memorably flawed, paranoid narrators sucks us in, and what starts off as a drunken lament, as sweet and bitter as an extended country and western song, slips seamlessly into the sort of big, consequential novel we've come to expect from a writer of his stature. It's the book that many hand-wringing liberals have always wanted to write but are manifestly ill-equipped to undertake. Try writing a novel tackling the themes of globalisation without critical reference to imperialism or capitalism and you're trying to hunt big game with a pea-shooter. The bad news for the narrow, effete stylists you'll see championed in magazines like the New Yorker is that Kelman seems the only English-speaking writer working in literary fiction who's got the vision, bottle and technical ability to nail it.

Typically, there are no structural concessions to the reader; you won't find a chapter break from the first word to the last, 437 pages later, the author trusting us to ration our own sittings. Having said that, this is one of the most accessible books he's written in a long time. You Have to Be Careful is tense and moving and in some parts even bawdy. It's also full of a humour that is always there to make a point, rather than being cheaply deployed for its own sake. Take this exchange between Jeremiah and an American barman:

"English?"

"Not at all, I'm Skarrisch."

"Skarrisch? Neat. Ever since I was a kid my dream is to go to your country, I mean from childhood."

"What like to emigrate?"

"Huh?"

"To go and live there?"

"To go and live there, no sir."

The sections immediately following and preceding this encounter say more about American and Scottish culture than volumes of bland pontification. And that's the recurrent theme of this novel: our identity and status within the globalised order. The "events of September the 11th" aren't mentioned once, as it's intrinsically understood that state paranoia about security and immigration long precedes them. This has the effect of making the rash of novels that put such events centre-stage seem like angst-ridden irrelevance or even just manifestly exploitative.

The novel is, and must always be seen as, an artefact. Kelman, more than any other writer, makes us forget that. That is the gift of a real artist, and it's got to the embarrassing stage that it's now very difficult to see which of his peers can seriously be ranked alongside him without ironic eyebrows being raised.

You Have to Be Careful in the Land of the Free will delight Kelman loyalists and should win him many converts among Americans who are tired of being spoon-fed from the narrow and stagnant cultural pool of the New York Times bestseller list. A good thing too, as this brave and provocative novel deserves to be widely read.

Irvine Welsh's most recent novel is Porno (Vintage). James Kelman appears at the Guardian Hay Festival on Saturday May 29. See www.hayfestival.co.uk for details.